Extend search logic for shared MKL library to look in user site

[haasad]

Expands on #45 to make it work for all operating systems

[haasad]

Successfully tested here:

• old behaviour with pip install --user: https://github.com/haasad/PyPardisoProject/actions/runs/3432111864
  • ImportError: Shared library mkl_rt not found
• new behaviour: https://github.com/haasad/PyPardisoProject/actions/runs/3432128582
  • works on all OSs